Lasagna

Lasagna is a great dish for beginners as well as experts! It can be as simple or as complicated as you want, and whatever level of effort you give it is reflected yet even the minimum amount of work is still tasty, so it's great for practicing your skills without worrying about ruining the dish. It's also great for cooking on a budget, or for entertaining because it makes so much so easily. I've thoroughly impressed large dinner parties with a laughably small amount of effort.

Components[]

Lasagna is made of four basic ingredients:

Noodles
Tomato sauce
Ricotta cheese
Mozzarella cheese

That's it! You can just buy those ingredients off the shelf, put them together (see below), and it will be delicious. Or, you can make each component as fancy as you want. If you're a novice, you can focus on just one component and make that a little fancier. Here's a breakdown:

Most Basic[]

No skill required, still very tasty:

Noodles -- buy dried noodles. One package is more than enough for one pan. Note: some companies make a "no boil" noodle that you put straight in the pan, and it cooks itself during the baking process. These save a ton of hassle, and you can't taste the difference compared to the regular noodles that need to be boiled first.
Tomato sauce -- buy a big jar of Prego or whatever. A regular jar may be enough for a small pan, but probably just barely. Just get a big one and be safe.
Ricotta -- buy the big tub (it comes in two sizes).
Mozzarella -- buy one bag of shredded.

A Little Fancier[]

Only incredibly basic skill required, but a huge step up in quality:

Noodles -- buy fresh pasta sheets. They can usually be found at an upscale grocery store such as Whole Foods. You'll have to boil these, but it only takes a few minutes.
Tomato sauce -- make store bought more interesting by adding meat. Ground beef and/or sausage (about a pound) are natural choices, just brown them in a pan and season (liberally) however you want. Salt and pepper as always, then basil, oregano, and fennel seed are typical Italian seasonings. Or just buy Italian sausage that's already seasoned. If the sauce you bought is plain, add a ton of basil and oregano to it. You can add the sauce to the pan with the meat if you want to flavor the sauce, or just add the meat separately to one or more of the sauce layers.
Ricotta -- dump the big tub into a large bowl, add two whole eggs and a ton of dried parsely flakes, and mix it all up. Makes it creamier and a lot more luxurious.
Mozzarella -- use fresh mozzarella. Either buy the little balls and sprinkle them on for the mozzarella layers, or buy the big chunks and slice it up. Fresh mozzarella is way better than the pre-shredded stuff in the bags; this upgrade makes a huge difference. You'll need about two of the big chunks.
Add a layer of spinach, eggplant, or whatever other vegetable you want. These will need to be cooked separately first; the baking process won't cook vegetables correctly, especially for something tough like eggplant.

Super Fancy[]

Some more advanced techniques required, though nothing crazy. Requires a lot of kitchen equipment, however.

Noodles -- make your own! It's actually not that hard, and you don't even strictly need a pasta roller machine (though it does make it easier). There are some great tutorials for making your own pasta on youtube, so I won't bother trying to explain it in text form here. There are a ton of little variations that you'll see if you browse multiple videos, but you'll get the idea pretty quick, don't sweat any little tricks that strike you as odd, or that you only see in one recipe/video. As an added bonus, you don't have to bother with cutting the pasta into noodles, forming difficult shapes like farfalle, sticking it together like ravioli or tortellini, or anything like that--the sheets just go straight into the pan (with a little cutting to make them fit)! If you don't have a pasta machine, just roll the dough out with a rolling pin, it's okay if lasagna noodles are a little thicker than you'd typically use for other types of pasta.
Tomato sauce -- make your own! Also not that hard, but a little time consuming and requires that you have a really good palate to get the spice balance right. In all honesty, you're not going to taste much of a difference above a good quality store-bought sauce once everything is baked together, especially if you did the stuff in the "A Little Fancier" section.
Ricotta -- make your own! Ricotta is the easiest cheese to make by far (it's pretty much just curdled milk), and fresh is way better than the tub. I'll leave it to you to look up how to make it. This might sound laborious but I promise it's well worth it.
Mozzarella -- (wait for it...) make your own! Mozzarella is also relatively easy to make, but is really not worth the effort over just buying it unless you're trying to show off that you made everything completely from scratch.

Assembly[]

You'll need a baking dish roughly 13"x9", with as high of walls as possible. Brownie pans overflow surprisingly quickly. Consider buying a disposable roasting pan.

Sauce goes on the bottom (yes you read that correctly, it sounds weird but it keeps anything from burning to the bottom of the pan), followed by noodles. After that, there's no real set order despite whatever any recipe you reference might say. I typically like to alternate sauce and cheese, separated by noodle layers, so (from the bottom):

Sauce - Noodles - Ricotta/Mozzarella - Noodles - Sauce - Noodles - Ricotta/Mozzarella - Noodles - etc.

Or you can just rotate through the layers:

Sauce - Noodles - Cheese - Sauce - Noodles - Cheese - etc.

I say "etc." but you'll probably run out of ingredients by about that point. If you run out of one ingredient first, don't worry, just use up your remaining ingredients in some sensible way to finish it off. The amounts listed in the "Most Basic" section should all run out at roughly the same time, and leave you with tons of extra noodles.

One word of caution -- Make sure there's a layer of sauce above your last layer of noodles, otherwise those noodles will dry up and get crispy. End with cheese on top.

Baking[]

After you've put everything together, bake it (350°F, 375°F, whatever) until it's hot all the way through and the cheese on top has started to brown (usually about 30 minutes, up to 45 minutes if you made a super thick pan). The baking isn't really cooking anything, it's just getting everything hot all the way through. Let it cool for a good 15 minutes after coming out of the oven so it can start to solidify, otherwise it will fall apart when you try to serve it.